MAg.sub.4 I.sub.5 (wherein M is a monovalent cation) is a high ionic conductivity solid electrolyte. Conventional MAg.sub.4 I.sub.5 preparation methodology involves the dissolution of MI in molten AgI. Stoichiometric amounts of MI and AgI are ground then melted in an alumina crucible above 560.degree. C., in flowing argon, then cooled to room temperature. The resulting ingot is then ground by ball milling for several hours to produce MAg.sub.4 I.sub.5 in powder form.
Commonly assigned, copending application Ser. No. 08/939,465, filed Sep. 29, 1997 discloses an AgI based photothermographic imaging system that utilizes the controlled decomposition of MAg.sub.4 I.sub.5 in acetone as the process to generate an imaging material. The MAg.sub.4 I.sub.5 reagent disclosed in the '465 application is generated by the above described conventional preparation methodology. This process requires high temperatures and numerous process steps. It would be desirable to produce the MAg.sub.4 I.sub.5 by a simpler method.
As discussed in the '465 application, MAg.sub.4 I.sub.5 can be used to generate light sensitive AgI for use in a photothermographic element. In preparing photothermographic elements as described in the '465 application, an organic solvent is used for forming the light sensitive imaging layer. It would be desirable to be able to use water as the solvent in preparing a photothermographic element. However, MAg.sub.4 I.sub.5 is unstable in water. It would be desirable to provide a stable aqueous composition containing MAg.sub.4 I.sub.5.